The problem can be corrected by upgrading the affected package to
version 4.0.23-3ubuntu2.4 (for Ubuntu 5.04), or 4.0.24-10ubuntu2.3
(for Ubuntu 5.10). In general, a standard system upgrade is
sufficient to effect the necessary changes.

Details follow:

USN-274-1 fixed a logging bypass in the MySQL server. Unfortunately it
was determined that the original update was not sufficient to
completely fix the vulnerability, thus another update is necessary. We
apologize for the inconvenience.

For reference, these are the details of the original USN:

A logging bypass was discovered in the MySQL query parser. A local
attacker could exploit this by inserting NUL characters into query
strings (even into comments), which would cause the query to be
logged incompletely.

This only affects you if you enabled the 'log' parameter in the
MySQL configuration.